Sea ice thickness in the southwestern Sea of Okhotsk revealed by a moored ice‐profiling sonar

Using a moored ice‐profiling sonar along with a moored acoustic Doppler current profiler, a total spatial section of draft across 3334 km of sea ice was obtained in the southwestern Sea of Okhotsk near Hokkaido in the winters of 1999–2001. Using this draft data set, the average draft and keel statistics are discussed in this sea for the first time. The mean draft was 0.60 m, which corresponds to the thickness of 0.71 m, over the three winters with the range of 0.49–0.72 m for each winter. The classification of level and deformed ice reveals a small range of the monthly mean level ice draft (0.18–0.27 m) and the dominance of the deformed ice in terms of volume (80%). The mean draft varied with the areal ratio of the deformed ice fairly well. These results suggest that dynamic processes such as ridging and rafting are important for the evolution of draft in the region of observation. The observed draft probability density distribution and keel statistics show that the thick ice ratio and keel frequency are lower than the similar data in polar regions and closer to those observed in Davis Strait west of Greenland. Along with the ice concentration and speed derived from the satellite data the southward ice transport to the southwestern Sea of Okhotsk is estimated on the basis of the observed sea ice thickness. The estimated ice transport ranged from 15 to 70 km 3 in each winter. The heat and freshwater transport associated with the ice transport ranged from −3.9 × 10 17 to −1.8 × 10 18 J and from 12 to 57 km 3 , respectively.